Might try using the deprecated gl_FragColor if this is a 130 shader or try explicitly declaring it "out gl_FragColor;". If that doesnt work try varying for your shader in's, ive never had problem on amd or nv with varying keyword for 130 shaders.

This is very annoying thing when it comes to shaders :\ I remeber in my early days when I tested my application on Nvidia card everything was ok, and I had problems with AMD. What solved my problems was changing doubles to floats (i.e. changing 0.0 to 0.0f).

I see you're using a for loop to dynamically get gLights[i].With GLSL I've had problems in which a shader worked fine on my desktop PC, but on my laptop wasn't giving proper results.

My fix was to manually unroll the loop...very tedious but it solved the problem.So instead of doing gLights[i] you'd do gLights[0], gLights[1] etc explicitely.

A general debugging tip by the way, is to comment out complex calculations and replace them with constant values you know should work. Do this until some form of logical graphical output appears, and work your way down from there until you pinpoint the issue.

This is very annoying thing when it comes to shaders :\ I remeber in my early days when I tested my application on Nvidia card everything was ok, and I had problems with AMD. What solved my problems was changing doubles to floats (i.e. changing 0.0 to 0.0f).

Depending on the version, GLSL requires you to put the f suffix on there. nVidia's GLSL compiler deliberately accepts invalid code, whereas AMD's strictly follows the specification. This is a good way for nVidia to use us developers as a marketing/FUD weapon, spreading rumours that AMD has bugs...

Seeing that GLSL code is compiled by your graphics driver, which may or may not be different to your user's driver, it's a good idea to run your code through an external tool to ensure it's valid, such as ShaderAnalyzer, glsl-optimizer, the reference compiler, etc...

Naah, the rumours started because AMD OpenGL implementation used to be really, really, REALLY broken. But that isn't the case anymore.Probably, nowadays it's true that NV makes look AMD wrong.But honestly, I despise what NVs does on that front, because it happens you can't rely on them (running invalid code not only breaks on AMD, Intel Mesa drivers on Linux are also quite good).

Naah, the rumours started because AMD OpenGL implementation used to be really, really, REALLY broken. But that isn't the case anymore.
Probably, nowadays it's true that NV makes look AMD wrong.
But honestly, I despise what NVs does on that front, because it happens you can't rely on them (running invalid code not only breaks on AMD, Intel Mesa drivers on Linux are also quite good).

is there a need to specify GLSL version to compile shaders with? If there is an advanced opengl distrubution on a system, will deprecated lower versions of GLSL code not compile?

The problem was in the attribute locations in the vertex shader. NV automatically generates those according to the order in which the attributes where defined, while ATI needs to have the explicit layout(location = index) in front of each attribute. Also I switched to #version 330 otherwise those layout() identifiers are not available. The version change is no problem since i want to implement a deferred renderer in the next step anyway.

This is very annoying thing when it comes to shaders :\ I remeber in my early days when I tested my application on Nvidia card everything was ok, and I had problems with AMD. What solved my problems was changing doubles to floats (i.e. changing 0.0 to 0.0f).

Depending on the version, GLSL requires you to put the f suffix on there. nVidia's GLSL compiler deliberately accepts invalid code, whereas AMD's strictly follows the specification. This is a good way for nVidia to use us developers as a marketing/FUD weapon, spreading rumours that AMD has bugs...

Seeing that GLSL code is compiled by your graphics driver, which may or may not be different to your user's driver, it's a good idea to run your code through an external tool to ensure it's valid, such as ShaderAnalyzer, glsl-optimizer, the reference compiler, etc...

It was during the time I used shaders for the very first time and 'I had no idea what I was doing' . Back then I was using shader designer btw.